The present invention relates to a glow-discharge decomposition apparatus, and the preparation of a semiconductor film employed in the glow-discharge decomposition apparatus.
In a conventional glow-discharge decomposition apparatus, a substrate 4 shown in FIG. 1 is horizontally provided on a ground electrode labelled 3, wherein a RF-electrode 1, heater 5, and the like are arranged in a way as illustrated in FIG. 1. The numeral 10 is a port from which the gases enter into the chamber. The numeral 11 is another port through which gases are evacuated by an evacuator. In such an apparatus, a semiconductor film can be widely deposited on a substrate, but an excess discharge takes place at a rear side of the RF-electrode. To avoid the discharge at the rear side, a shield 7 must be prepared as in FIG. 1, but such a shielding results in an unstability of a glow-discharge.
An apparatus shown in FIG. 2 is arranged for two-side deposition and is free from the shielding. In the apparatus, substrates 41 and 42 are vertically provided on ground electrodes 31 and 32, and a RF-electrode labelled 1 stands at the center of the ground electrodes. A glow-discharge takes place over both sides of the RF-electrode 1. If necessary, substrates 41 and 42 are heated by heaters 51 and 52. In such an apparatus, only one RF-electrode 1, one RF-power supply 9 and one matching circuit 8 can be prepared, although two substrates are placed. However, the apparatus represents a certain handicap wherein the deposition rate on the substrate cannot be independently controlled when the required deposition rates on both sides are very different from each other.
To control the individual power to the RF-electrodes, an apparatus can be designed in which two substrates stand in the center of a chamber, two RF-electrodes 11 and 12 face the two substrates, respectively, and two independent RF-power supplies 91 and 92 and matching circuits 81 and 82 are provided as in FIG. 3. Individual control of the discharge is realized by adjusting every electric output power, to control the deposition rates. However, there might be an interference between RF-power supplies which supply RF-powers to each electrode. Furthermore, two RF-power supplies and two matching circuits are needed, so that the apparatus as disclosed above, due to its complexity, costs too much and establishes some limitations.
An object of the present invention is to provide a glow-discharge decomposition apparatus which gives different or same depositing rate on each substrate by an individual control of RF-powers supplied to each electrode with one RF-power supply and one matching circuit.